With the development of the science and technology, the use of a portable electronic apparatus (e.g. a mobile phone, a tablet computer, etc.) already becomes more and more popular. Different from a common electronic apparatus, for the sake of portability, the shape of the portable electronic apparatus is usually designed to be light, thin, and small. Accordingly, the size of the speaker embedded in the portable electronic apparatus also decreases gradually. However, due to decrease of the size of the embedded speaker, the sound quality usually becomes worse, so some users who have high requirements for the sound quality become unsatisfied.